The strongly pro-government sections of the UK media, not least the Mail and Express, will by tonight - in all probability - be fulminating about the "thugs and trouble-makers" who have taken to the capital's streets to show that the alternative to a massive delayering of the national and local state and swingeing cuts in public services is... well, hooliganism. This will be the case even if it is tiny handful who misbehave, and in spite of the fact that hundreds of thousands will peacefully join the TUC-led march against the cuts, and their impact on the poorest and most vulnerable in society.
This is what some sections of the press are interested in, as part of a politically rather than journalistically motivated campaign: finding anyone with a stick, bottle or stone who can be used for a dramatic photograph to tar all opponents of the government's policy as violent malcontents.
The same tactics are being and have been used to seek to discredit overwhelmingly peaceful protests in Egypt, Tunisia, Bahrain and Syria.
The police (whose own public order strategies have been criticised of late) have also said that they fear, and are preparing for, violence from a minority. And education secretary Michael Gove used his BBC Radio 4 'Today' programme interview this morning to sound portentous about the 'dark underside' that may emerge. The narrative is being prepared.
It is very much to be hoped that the few hotheads who often attach themselves to large, peaceable public protests do not seek to mar this one and act up for the eager cameras. If they do, they will be undermining rather supporting the strong moral cause of seeking an alternative to an economic strategy which makes those with least pay for an economic and environmental crisis presided over by those with most.
But it is also very difficult, short of security-state tactics, to stop disorder altogether in large gatherings - whether at a demonstration, at a football match or in a shopping mall. Such antics are not the main point, however. Those who eagerly try to write otherwise have causes other than truth and decency in mind. And when, with sad predicability, they attempt to do so, you read it here first.
Subsequent report: "Major disputes over Trafalgar Square 'riot' claims after demo" - http://www.ekklesia.co.uk/node/14422 
(c) Simon Barrow is co-director of Ekklesia.